During use, aircraft engines are subject to a number of external influences, which can lead to components becoming worn. Such wear can affect the front seal plate, for example, which is provided in an aircraft engine inter alia for sealing a bearing unit. By means of such bearing units, the shafts provided for power transmission are mounted in aircraft engines. Depending on the engine model, two or three shafts are generally used.
An example of a two-shaft engine is the Pratt & Whitney 4000 (PW4000) engine model. An inner N1 (low-pressure) shaft here serves to transmit power from the low-pressure turbine to the low-pressure compressor, and a second N2 (high-pressure) shaft that surrounds the N1 shaft coaxially transmits power from the high-pressure turbine to the high-pressure compressor. At its front end associated with the low-pressure compressor, the N2 shaft is mounted in the engine shroud by way of a bearing unit. When that bearing unit and/or the front seal plate arranged close to the bearing unit have to be exchanged, for example because of wear phenomena, this is carried out according to a known specified sequence.
This known sequence provides that the engine must first be detached from the wing of the aircraft in order subsequently to be transported to a workshop. The known method will be explained briefly with the aid of FIG. 1. In the workshop, the low-pressure turbine 7 is separated from the remainder of the aircraft engine 1 in a first major step. In the case of the PW 4000 engine, the low-pressure turbine 7 comprises the N1 shaft 3 and the turbine exhaust case. In order to dismantle this component assembly, a large number of conduit systems and further components must be removed from the aircraft engine 1. Overall, separation of the component assembly from the remainder of the engine is complex.
The core engine 6 is then removed from the engine, the core engine 6 also including the bearing unit 2 that is to be exchanged and the front seal plate. The core engine 6 generally further comprises the high-pressure compressor 30, the combustion chamber 31 and the high-pressure turbine 29.
There remains a cylindrical cavity in the core engine 6, because the N1 shaft 3 has to be withdrawn from the core engine 6 in the course of the separation of the low-pressure turbine 7 from the remainder of the engine.
When the core engine 6 has been removed, and after further components, such as, for example, the front seal plate nut, have been dismantled, the front seal plate and the bearing unit 2 to be repaired or changed can be unscrewed or removed from the N2 shaft 4. After the components have been repaired or exchanged, they are pushed or screwed onto the N2 shaft 4 again and the aircraft engine 1 is assembled again by a mounting process which corresponds substantially to the dismantling process in reverse.
This known method is very complex and expensive, in particular because the engine has to be dismantled to a large degree in order to exchange the bearing unit and/or the front seal plate. In particular, it is not possible to exchange a front seal plate “on-wing” on an engine that is still attached to the aircraft wing.
Accordingly, the object underlying the invention is to provide a method for changing a bearing unit in an aircraft engine in which the bearing unit can be exchanged with a reduced outlay.
The invention achieves that object with the features of the independent claims. Further preferred embodiments of the invention are to be found in the dependent claims, the figures and the associated description.